The prior art method of manufacturing crystalline silicon solar battery module includes connecting the crystalline silicon solar batteries in parallel or series by a conductive soldering strip. Prior art methods then encapsulation the connected crystalline silicon solar batteries in front and rear module panels by hot-pressing them together so as to meet the requirement of windproof, dustproof, moisture proof, and corrosion resistance in the process of using crystalline silicon solar battery modules.
However, due to the difference of the thermal expansion coefficient, crystalline silicon solar battery will exhibit different bending degrees and can cause great difficulties in the production of crystalline silicon solar battery modules after the electrodes of crystalline silicon solar battery are soldered to the conductive soldering strip. More seriously, under pressure from the conductive soldering strip, the crystalline silicon solar battery can crack easily, and sometimes in hidden places of micro-cracks after the connection and reduce the photoelectric conversion efficiency of crystalline silicon solar battery module.
One remedy to solve the problems described above is to reduce the thickness of the conductive soldering strip. The conductive soldering strip can become softer with reduced thickness; therefore, the micro-cracks and bending problem of crystalline silicon solar batteries can be improved after being soldered to conductive soldering strip.
Unfortunately, after reducing the thickness of the conductive soldering strip, the effective conduction area of the conductive soldering strip can decrease accordingly and cause an increase of series resistance of crystalline silicon solar battery modules. This can even result in the power loss from crystalline silicon solar batteries to the crystalline silicon solar battery module. In the production of crystalline silicon solar battery modules, the loss of photoelectric conversion efficiency from the crystalline silicon solar batteries to the crystalline silicon solar battery module is between about 3-5%. With the increase of photoelectric conversion efficiency of crystalline silicon solar batteries, especially with the increase of short-circuit current of crystalline silicon solar batteries, the loss of photoelectric conversion efficiency from the crystalline silicon solar batteries to the crystalline silicon solar battery module tends to be more serious.
A solution to the loss of photoelectric conversion efficiency from the crystalline silicon solar batteries to the crystalline silicon solar battery module is to replace the conventional heat soldering technology with laser soldering technology. Compared with traditional soldering technology, laser soldering technology has advantages of short heating time, precise control of heat input and small heat affected zone, which effectively avoids the micro-cracks and bending problems of crystalline silicon solar batteries caused by the difference of thermal expansion coefficient. Therefore, after adopting laser soldering technology, the thickness of conductive soldering strip can be increased so as to effectively reduce the efficiency loss of photoelectric conversion from the crystalline silicon solar batteries to the crystalline silicon solar battery module.
One condition of soldering the conductive soldering strip to the crystalline silicon solar battery is that the conductive soldering strip may have to be contact physically to the electrodes of crystalline silicon solar battery. The purpose of this contact is to transfer the heat on the conductive soldering strip to the electrodes of the crystalline silicon solar battery as quickly as possible so that the molten alloy can wet; then cool and solidify on the electrodes of the crystalline silicon solar battery. In the end, the conductive soldering strip can be soldered with the crystalline silicon solar battery.
Because laser soldering is a type of non-contact soldering, the method can be achieved when the physical contact between the conductive soldering strip and the crystalline silicon solar battery can be made, which may be the key point of adopting laser soldering technology to solder crystalline silicon solar batteries. The patent application CN101884114A disclosed a method to tightly contact the conductive soldering strip to the electrodes of crystalline silicon solar battery. However, the surfaces of the conductive soldering strip and the electrodes of crystalline silicon solar battery are not very smooth. As a consequence, the conductive soldering strip failed to contact tightly to the electrodes of crystalline silicon solar battery in some local areas and affected the reliability of laser soldering.
Due to the problems described above, laser soldering technology remains in the laboratory research stage and has not been applied in production of crystalline silicon solar battery module.